A mobile handset has to keep the frequency of its local oscillator close to the frequency of the signal it receives from the base station. This is required in particular in orthogonal frequency division multiplexing (OFDM) systems like WiMAX (worldwide interoperability for microwave access), 3.9G or digital video broadcast (DVB) systems etc.
OFDM systems promise high data rates with low complexity due to the simplicity of the fast Fourier transformation (FFT) and one-tap propagation channel. However, this can be assured only if the receiver is in a synchronization mode. A drawback of OFDM systems is that they are very vulnerable to frequency errors. That is why many kinds of accessories are needed around the FFT to keep it accurately in the synchronization mode. If not designed carefully, the synchronization algorithms can significantly increase the complexity of the receiver.
The difference between the base station transmitter frequency and the locally generated frequency at the handset is called the carrier frequency offset (CFO). WiMAX has its roots in the fixed networks. The deployment of WiMAX in mobile cellular environment will cause the handsets to experience lots of interference from neighbouring cells. Many prior art CFO estimation methods may suffer from interferences coming from other base stations or cells.
The mobile WiMAX system is such a new system that there are no conventional methods easily available. There is at least one method available which is similar to those used in WLANs. However, such a method suffers from other-cell interferences.